A brief introduction of the main causes and features of classic material fatigue of rolling bearings was presented along with some of the ramifications of using bearing grade steel in structural fatigue type applications, such as shafts.

Bearing steels will typically realize high scatter in fatigue results, relative to ductile steels, whether used as a bearing or as a structural machine member. Fatigue scatter with bearing steel is due largely to the inconsistent existence of sub-surface non-metallic inclusions randomly located within the volume stressed of the otherwise very strong microstructure. The effect of inclusions follows the fact that these very high hardness steels are highly notch sensitive, thus it is expected that the fatigue durability of these materials will be greatly diminished by surface imperfections as well as sub-surface inhomogeneities.

Recent INA USA VPD activities support these conclusions from real testing with bearing grade SAE52100 under finite life fatigue test conditions. It was shown that for these initial finite life VPD validation studies, good fatigue assessment correlations using fe-safeTM were made when considering L50 median life. More testing should be made with SAE52100 to increase confidence in the VPD methods used.